Multiple vacuum inlets are frequently required for industrial purposes to remove dust and other light trash at work stations, and for domestic and other purposes where it is more convenient to carry a vacuum hose to an inlet than it would be to transport a powered suction unit along with the hose. Many inlets can be connected to one vacuum conduit, but if more than a few are connected along one length of the conduit, some basic problems have to be faced. There is a need for the diameter of the conduit to be large enough to permit passage of the sum total of all the air from the inlets when they are all open, and yet small enough to keep the air moving through the conduit at a speed sufficient to move trash along the conduit instead of letting it settle to the bottom of the conduit where it extends horizontally. If the conduit diameter is too small for the number of inlets when all are open at once, there will be insufficient vacuum differential pressure at some of the inlets furthest upstream. If the conduit diameter is too large, either along all of the conduit, or near its downstream end, there may be insufficient movement of air to keep the trash moving when only a few of the inlets are open.
All this has led conventional designers of such equipment to subdivide large numbers of inlets into separate systems each having a limited number of inlets connected through a common conduit to a separately powered vacuum unit. This is expensive, and can result in shutting down all of the inlets in one such subdivision when its power unit ceases to operate for any reason.